Timing on 620" BBC

[lmchevy]

Where would you run your timing on a 14.8-1 620" BBC and be safe.It is carburated on gas and n/a.Thanks

[topcat572]

I ll get the ball rolling for the other guys to chime in, What head are You running, I hear the ones with the smaller chambers use less timing,Anyone? I run 37 now on a 572 conventional head.

[lmchevy]

I have the Pro1 355 cnc heads.119cc chambers.

[bjuice]

i have a 632 with 14 degree big chief heads on gas...it likes 34.

as they say start off conservative and work up...i will go out on a limb and say 32 would be a ( extra) safe place to start and go from there if it were mine and no dyno records to show sweet spot with timing

Brian

[hammertime]

I used to put my gas motors around 39-40, on the dyno last year my motor shop at the time started at 32. I sat back and just watched sure enough it made more hp at 34 then at 39. Every motor is different

[LuckyDawgRacing]

I'm at 36 on alky

[tcarda]

Where would you run your timing on a 14.8-1 620" BBC and be safe.It is carburated on gas and n/a.Thanks

My engine that has 355 heads on it likes 38. Is there a engine dyno you can take it to and find out what it likes?

[lmchevy]

Tcarda i probably could go and put it on a chassis dyno.

[bjuice]

Tcarda i probably could go and put it on a chassis dyno.

chassis dyno probably would not tell you what your looking for since there is no telling how much HP is being lost thru the chassis.
my advise is save your time and money on the chassis dyno for this purpose.


Brian

[Tod74]

Tcarda i probably could go and put it on a chassis dyno.

chassis dyno probably would not tell you what your looking for since there is no telling how much HP is being lost thru the chassis.
my advise is save your time and money on the chassis dyno for this purpose.


Brian

That's a good point but I have a question.
Wouldn't the chasis dyno still allow you to see a gain or a loss from a timing adjustment? I mean, regardless of what it is making at the crankshaft, if it is showing say 500 hp 400 ft lbs on the chasis dyno, and you advance the timing 1 or two degrees, then run it again, take a reading,then retard it and run it again..take another reading...wouldn't this allow you to find the timing that makes the most power?
Regardless if the hp numbers are bogus...as long as they are consistantly bogus...wouldn't that allow you to find the tune up?
Not arguing here...just asking.

[bjuice]

if the car acted the same at 400 hp as it does at 500 hp and 600 700 hp...you could get an idea..but since chassis act so differently under specific loads it would be a tough way to guess the sweet spot for Hp at the crank..

we were at the track last night..my cousins Nova didn't like 1 gun (250shot) it upset his chassis..he came back on a 2nd run pulled triggers on both guns for a total of 500 shot and the car laid down a pass..
a chassis dyno is a good tunning tool for the CHASSIS by trying to stop the hp loss thru the chassis by experimating with pionion angle,TQ converters,gear changes,tire sizes...list goes on and on...the key thing is that before most chassis dyno sessions *if done for right reasons) already know thru a motor dyno session how much optimal HP/TQ a motor will make at the crank..you will never exceed this number by chassis tweaking...but the goal is to reduce as muc hp loss thru the chassis by tweaking the chassis,drive train etc...

i do agree there may be a hint of more hp to the rear wheels by re-adusting the timing..but as my cousins senerio i mentioned above..did the motor make more hp and lost it thru the chassis for excessive flex or whatever reason, OR did the motor make LESS hp but showed more at the rear wheels beacuse the chassis is not as agitated...etc...


i guess my point is.. your trying to find max hp and optimal TQ at the CRANK at a selected timing..not to mention certain temps etc....

although there are certain indicators such as chassis dynos...its not a sure fire bet you will get the accurate ino beacuse of the variables invloved from the flywheel to the rear tires...

of course this is justs my opinion only...


By the way Richard childress has used some chasiss dyno sessions on some of their cup cars and one of the more notable findings they reported in their session was for every degree of pinion angle equaled approx 10 hp loss

i would personally start that 620ci at 31/32..and go from there..or spend $600 for a motor dyno and know 100%

[sc3314]

I agree with Brian here, don't waste your cash on a chassis dyno at this point for a timing issue. Like he said so much can be lost at the rear wheels you would never see the change in a few degrees of timing.

You may only gain 10 to 12 HP on a dyno with a timing change from 32 to 38 depending on the motor. I would start at 32 and work your way up, till the car slows down. Watch your plugs, and make sure you do every thing the same. Tire pressure, burn out, launch rpm, shift points, fill the fuel cell every pass.

The cost of building these motors any more $600.00 to put it on a dyno is nothing compared to what you learn about the motor on a dyno. Putting a pump gas 555 on the dyno in a few weeks. I' am hoping it will make 800 to 825 hp with a final C/R of 10.5